Figure 3.

Patterns of expression of L1 RNA, ORF1p, and ORF2p during
spermatogenesis. Available data suggest that the synthesis of full-size
L1 RNP consisting of FL-L1 RNA, ORF1p, and ORF2p is repressed during
spermatogenesis. No L1-related products have been found in spermatogonia.
Transient expression of FL-L1 RNA and ORF1p (but not ORF2p) occurs in
spermatocyte I at the onset of meiosis (leptotene through mid-pachytene stage
of prophase I). These upregulated FL-L1s are implicated in chromosome pairing [145]. Transcription of L1s resumes in spermatocyte II and continues in
spermatids. However, L1 RNAs are mostly short, spliced, and prematurely
polyadenylated species that translate into either ORF1p or ORF2p. Their
functional significance is not known. Transcription of L1s, ORF1p, and ORF2p is
downregulated by the spermatozoa stage. A small amount of FL-L1 RNA (not
detectable by Northern blotting) is available in spermatozoa. ORF2p, not found
in testicular spermatozoa [18], is detectable in the sub-acrosomal space in mature sperm [27].